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PostPosted: May 26th, 2022, 4:16 pm 
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Joined: June 22nd, 2013, 11:00 am
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Does, for example, having four equal driver's running series-parallel have any differences if the are ran parallel-series. They both come out to the same impedance, but is there any other intended or unintended changes?

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PostPosted: May 26th, 2022, 8:52 pm 
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Joined: February 28th, 2013, 1:19 pm
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Good question. Electrically, there should be no difference, both the composite voice coil resistance and inductance should be the same in either case. If the drivers are electro-mechanically the same, then you should get equal load sharing between them. They should have the same impedance as a single driver, but with an increase in efficiency (+6dB, I believe). Now there may be some difference in how driver inequality is handled between the two arrangements with respect to load sharing between each pair. Worth experimenting to see which sounds the best.

David


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PostPosted: May 27th, 2022, 7:53 am 
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There is a concern with putting dynamic drivers in series and that occurs at resonance. If you look at a typical impedance curve, two things happen at resonance. First, the phase goes from leading to lagging. Second, the impedance reaches a peak that can be ten times or more than the impedance at other frequencies. If the drivers in series have different resonant frequencies (Fs) they will get out of phase. That is the movement of the cones will not be in sync, with one leading the other. I have used a stroboscope to view this situation and it is real. The result is a drop in output at that frequency.

The second problem is that the high impedance of the drivers at resonance interferes with the ability of the amplifier to damp motion of the cones. Unless you have a servo system with only one driver, the amount of current the amplifier can provide into the driver decreases dramatically with the impedances that occur at resonance. You then effectively have two or more generators in series that are not in phase.

I have used drivers in series very effectively as long as they are used higher than the range of resonance. They are then both lagging in phase and have much lower impedance. Looking at them with a stroboscope, they are then in phase and there is no change in response beyond what a single driver would have.


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